JavaScript setTimeout runs fine on some object types by not others?

This might be best explained with a code example...

Object_A = {
  testLoop:function(){
             log("running");
             setTimeout(Object_A.testLoop, 1000);
           }
};

Object_B = function(){
  this.testLoop= function(){
    log("running");
    setTimeout(this.testLoop(), 1000);
  }
}

Object_A.testLoop(); // logs message to console every 1000ms, as you would expect开发者_如何学Go

var objB = new Object_B();
objB.testLoop(); // runs infinitely at once (no 1000ms interval) until "Maxium call stack size exceeded"

Why is it that the loop works fine in a static object but not in a "class-like" object that declares a generating function?

(on a sidenote: what it the correct name for these two types of object? I keep saying "satic" and "non-static" objects, but I feel like that's incorrect.)

Functions are first-class citizens in JavaScript. Given a function defined like this:

function foo()
{
    return 0;
}

There is a difference between this:

var result = foo();

and this:

var result = foo;

The first one invokes the function named foo and assigns the value returned by that invocation to result. In this case, result will be equal to zero.

The second one assigns result to the function named foo. Now, result is not equal to zero; result is equal to the function foo.

Do you see the problem in your code now?

setTimeout(this.testLoop(), 1000); should be setTimeout(this.testLoop, 1000); as you want the function, not its return value.

change this line

setTimeout(this.testLoop(), 1000);

to

setTimeout(this.testLoop, 1000);